This invention relates to a metering valve for dispensing a measured quantity of an aerosol from an aerosol container which is pressurized by a compressed gas such as air, nitrogen, or carbon dioxide.
Valves for this purpose are well known, and a typical example of such a prior art dispensing valve is disclosed in British patent application of Bespak PLC No. 2,178,398, published Feb. 11, 1987 as described in detail hereinafter. The invention is particularly concerned with such valves which include a metering chamber inside the container and a valve stem movable between a charging position wherein it connects the metering chamber with the interior of the container in order to fill the metering chamber with aerosol, and a dispensing position wherein it disconnects the metering chamber from the interior of the container and connects it to the dispensing outlet.
A problem which is common to all prior valves of this type is that although the metering chamber is initially charged with a dose which is under the same pressurized conditions as the other contents of the container, when the metering chamber is shut off from the interior of the container and connected to the atmosphere, the discharge of the metered dose is simply the result of the dissipation of the pressure force which was stored in the metering chamber, and which therefore constitutes a rapidly declining force.